1. Field of the Invention
The present invention relates to plate-end processing methods and blasting devices used in such methods, and more particularly, to a plate-end processing method suitable for processing, e.g., slight-chamfering or deburring an edge formed at the end of a plate, specifically, a plate composed of a hard, brittle material such as a glass plate, and to a blasting device used for performing the method.
2. Description of the Prior Art
A plate obtained by cutting out a large plate, such as a metal plate, a glass plate or the like has a sharp edge at the end thereof. In the case of a metal plate or the like, burrs may be adhered to the end thereof. If a person directly touches such a sharp edge or burrs with his/her hand, he/she could possibly hurt his/her hand, or if an object comes into contact with such a sharp edge or burrs, the object could possibly become scratched. Therefore, the end is generally processed by, for example, deburring or chamfering for removing the sharpness from the edge.
In particular, with regard to a plate composed of a hard, brittle material, such as a glass plate, a quartz plate, a sapphire plate, a ceramic plate, or a silicon wafer, if the plate still has a sharp edge even after the side surface thereof is mirror-polished, the edge tends to chip easily. Therefore, when bending stress is applied to such a plate composed of a hard, brittle material, the entire plate may readily crack starting from the chipped section on the edge.
Therefore, edge processing, such as edge chamfering or slight-chamfering of such a plate composed of a hard, brittle material, is important for increasing the strength of the plate.
With regard to a glass plate used as the aforementioned plate, the glass plate may be used as a substrate for a flat display, such as a liquid crystal display or a plasma display. For such intended usage, the demand for thin glass plates is increasing. As a result, it is necessary to process the end, such as the edge, finely with high accuracy. For example, it is necessary to perform slight-chamfering at a 0.5-mm width or smaller accurately and precisely without errors.
In the related art, slight-chamfering is generally performed on a plate by inserting an end of a plate 100 into a groove 111 of a rotating grooved grindstone 110 so as to grind the end as shown in FIG. 9, or by bringing each edge 101 at the end of the plate 100 into contact with a flat surface 121 of a rotating grinding wheel 120 as shown in FIG. 10. With regard to this chamfering process performed by bringing the end into contact with the flat surface 121 of the rotating grinding wheel 120, Japanese Patent Laid-Open No. 2011-26195 proposes another example of a method in which two grinding wheels 120 and 120 tilted relative to flat surfaces 102 and 103 of the plate 100 are provided such that the edges 101 are chamfered by grinding the end of the plate 100 interposed between the grinding wheels 120 and 120 as shown in FIG. 11.
Sandblasting is a known type of a cutting process for processing a surface to be processed of a workpiece by ejecting abrasive grains thereto together with compressed gas. Such sandblasting is sometimes performed on, for example, an end of a plate so as to remove the sharp edges therefrom, thereby obtaining a rounded end.
If the chamfering process is to be performed by using the grooved grindstone 110 as shown in FIG. 9 from among the aforementioned grinding methods, since the grindstone 110 and the edges 101 of the plate 100 are in point-contact with each other, the grindstone 110 becomes abraded relatively quickly or becomes jammed at these contact areas.
If such an abraded or jammed grindstone 110 is continuously used, a significant variation will occur between products processed before and after the occurrence of the deformation or jamming. Thus, the method cannot be used for processing glass plates that are to be used in the field of flat displays, which need to be processed finely with high accuracy.
Therefore, with regard to a grindstone that is abraded or jammed at the areas in contact with the plate, the grindstone needs to be replaced even if other areas thereof are not abraded or jammed. Due to this reason, in order to increase the processing accuracy of the grinding process based on this method, the grindstone needs to be replaced frequently, leading to an increase in costs.
On the other hand, in the method in which the chamfering process is performed by pressing each edge 101 of the plate 100 onto the flat surface 121 of the rotating grinding wheel 120 as described above with reference to FIG. 10, local abrasion of the grinding wheel 120 can be prevented so that the lifespan thereof can be extended, as compared with a case where the grinding process is performed by using the grooved grindstone 110 described above with reference to FIG. 9.
However, this method is problematic in that the plate 100 may become warped due to a processing pressure applied to the plate 100 for pressing the edge 101 onto the flat surface 121 of the grinding wheel 120, and in that both edges 101 and 101 at the top and bottom sides of the plate 100 need to be processed individually. This results in lower workability as compared with the method shown in FIG. 9 in which both edges can be processed simultaneously.
In the method discussed in Japanese Patent Laid-Open No. 2011-26195, the edges 101 and 101 formed at the top and bottom sides of the plate 100 interposed between the two grinding wheels 120 and 120 are simultaneously removed so that the chamfering process can be performed efficiently. In addition, the processing pressures applied to the plate 100 are counterbalanced so that the plate 100 is prevented from warping, whereby the aforementioned problems in the grinding method described above with reference to FIG. 10 are solved.
However, in the method discussed in Japanese Patent Laid-Open No. 2011-26195, if processing pressures F1 and F2 applied by the two grinding wheels 120 and 120 are not properly balanced, the edges 101 and 101 cannot be processed uniformly, and the plate 100 may possibly become warped.
Although this can be generally said with regard to grinding a hard, brittle material by using a grindstone, when grinding a plate composed of a hard, brittle material such as a glass plate, various kinds of cracks such as large or small cracks or chipped section/s generally likely to occur (occurrence of such cracks or chipped sections will be collectively referred to as “chipping” hereinafter). In addition, cracks or small cracks called micro-cracks tend to form readily due to impacts caused during the cutting process. The occurrence of such chipping or cracks significantly reduces the bending strength of the plate starting from the fracture when bending stress is applied to the plate. On the other hand, it is difficult to remove the chipping and the cracks completely by the grinding process.
The occurrence of such chipping or cracks can be suppressed to some extent by supplying an abrasive liquid, such as water or oil, between the grindstone and the workpiece. However, when the abrasive liquid is supplied in this manner, a mixture of the abrasive liquid and cut dusts adhere to the surface of the workpiece so as to contaminate the workpiece. Therefore, an additional step for cleaning the workpiece after the grinding process becomes necessary, resulting in an increased number of steps, which in turn results in an increase in workload, leading to an increase in cost required for processing and end of the plate.
As described above, sandblasting is sometimes used when giving the plate a rounded end by removing the edges therefrom.
However, in a generally known sandblasting process, the surface of the processed workpiece is satin-finished and thus cannot be planarized with high accuracy. In addition, cracks or micro-cracks are formed on the processed surface due to an impact generated when the abrasive grains collides therewith. Therefore, using the generally known sandblasting process for grinding a plate composed of a hard, brittle material such as a glass plate, leads to, for example, rather lower bending strength. Thus, sandblasting is not used for a chamfering process intended for increasing the strength of a plate composed of a hard, brittle material, or for a grinding process intended for removing cracks and micro-cracks.
In addition, in the generally known sandblasting process, it is difficult to make the abrasive ejected together with the compressed gas collide with a specific area. Therefore, if the sandblasting process is to be used for chamfering the aforementioned edges, not only are the chamfered sections processed, but also surrounding areas thereof extending several millimeters to several tens of millimeters therefrom are processed, making it impossible to perform the process with high accuracy.
Therefore, in the cutting process based on sandblasting, if a small specific area of the workpiece is to be cut, as in the slight-chamfering process, it is necessary to mask the areas that should not be processed so as to protect these areas. Consequently, a complicated process such as attaching a masking material to the workpiece and removing the masking material after the grinding process, is required.
Moreover, in the generally known sandblasting process, since the abrasive grains and the cut dusts adhere to the workpiece, a step for cleaning the workpiece after the cutting process is often required, resulting in an increased number of steps.
The present invention has been made to solve the problems in the related art described above. Specifically, an object of the present invention is to provide a plate-end processing method that can be widely applied to plates composed of various kinds of materials, can prevent the occurrence of chipping or cracks even if the workpiece is a plate composed of a hard, brittle material, allows for fine, highly-accurate processing (for example, slight-chamfering at a 0.5-mm width or smaller, preferably, extremely fine slight-chamfering at about 0.1-mm width) performed uniformly on a specific required area without having to perform a pretreatment, such as masking, allows for an economical process with small grindstone wear and abrasive grain consumption or the like, and prevents foreign particles from adhering to the workpiece so that a cleaning step after the process can be omitted.